Coated metal sheet and method of making the same



Sept. 9, 1958 R. KAPLAN ETAL 2,851,372

comm METAL SHEET AND METHOD OF MAKING THE SAME Filed Aug. 14, 1946 xii?rah [UP 5 ER? 74 44 f0 WARD /V. \SPfA/Mo rw EZZFE.

F? .1 1 /2 c m /3 /4 7 /5 /6 k Q l 11 1 04 L Ig atent iiice 2,851,372Patented Sept. 9, 1958 CUATED M TAL SHEET AND lbiETl'iUl) 01F MAKING THESAME Robert Kaplan, Chicago, and Edward N. Sienko, Clarendon Hills,111., assignors to Sun Steel Company, Chicago, 1th., a corporation offilinois Application August 14, 1956, Serial No. 603,9ti3 5 Claims. (Cl.117-8) This invention relates to the treatment of coated metal sheetsand products obtained thereby, and more particularly, to the treatmentof metal sheets coated with thermoplastic coating materials, andproducts obtained thereby, which may be used for decorative orstructural purposes.

The instant invention is particularly concerned with the handling ofcoated carbon steel sheets and coated sheets of the so-calledrust-resistant metals (i. e. copper, aluminum, stainless steel, etc.),although the instant invention may be used with any type of metal sheet,particularly any type of metal sheet that possesses cold formability atleast as good as the carbon steel sheets here employed. Therust-resistant metals have been used in sheet form for decorativepurposes and/ or structural purposes for a number of years. Therust-resistant sheets such as aluminum and stainless steel sheets havealso been embossed in small strips to provide ornamental sheets. Thesesheets have been coated, after they are embossed, with various coatingmaterials and, although the coating materials appear to be rather wellanchored because of the irregular embossed surfaces of these metalsproblems are often presented in connection with completeness of thecoating or continuity of the coating because of the many fine grooves orcuts in the embossed metal. Adherence of the coatings is sometimesimpaired also because of bending of the embossed materials.

In addition, the instant invention is concerned with the so-calledcoined thermoplastic coatings on sheet metal, wherein embossing of thecoating only is accomplished and the metal sheet itself is not deformed.Heretofore, such a coating Was first produced in the form of a thincoherent separate film which was embossed to the extent desired and thisfilm was then caused to adhere to the sheet metal by the use ofadhesives. The adherence between such coatings and the base sheet metalhas, however, left something to be desired, when the base metal issubjected to differences in temperature and/or is bent or otherwiseformed. The instant invention resides in part in the concept of applyingthe thermoplastic coating to the base metal (then'heating the same toits fusion temperature and cooling), and then embossing or coining onlythe coating itself (without deformation of the metal sheet), so as toobtain distinctly superior adherence between the-coating and the basemetal. The instant invention also resides in the application of thethermoplastic coating to the base metal sheet, followed by heating ofthe coating to approximately its fusion temperature for a brief periodthen cooling, and then embossing the coated sheet so as to deform onlythe coating or to deform both the coating and the metal sheet. Ineithercase superior adherence between the coatingand the sheet is obtained.

To the best of our know1edge,.others'in the industry havenot heretoforeembossed carbon steel sheet. The problemsof applying a coating to asheet so as to obtain adequate adhesion therebetween for most purposeshave also not been solved by prior workers in the art. As will beappreciated, this is particularly important with respect to carbonsteel, because carbon steel is not a rust-resistant metal and a coatingapplied thereto should provide protection against corrosion as well asthe desired ornamental effect.

As is well known, there are a number of other problems involved in thehandling of sheet steel, usually in the form of hot rolled sheets ofcarbon steel, i. e., steel wherein the principal alloying element iscarbon or steel of the SAE 1000 series. One of the properties ofparticular importance in the SAE 1000 series steelis cold formability.Cold forming or cold working of steel is contrasted to hot working inthat the mechanical treatment of steel in such working is carried outbelow the critical range. The cold working of steel involves a number ofoperations including cold forming, which may involve merely bending orstamping, or which may involve the relatively more diflicult operationof drawing.

In drawing, a generally flat sheet of metal is subjected to bendingcombined with a shearing force, but the metal having good drawingquality yields to the shearing force to the extent that it is deformedin drawing rather than being sheared or cut. If a metal is too brittleit breaks in such an operation. The metals used in the practice of theinstant invention are no more brittle than the carbon steel sheet hereemployed and preferably are substantially less brittle. In generaldrawing involves the formation of a dish-shaped article from a generallyfiat metal sheet and this operation is contrasted to more stamping orbending in that the metal having deep drawing quality is capable ofbeing drawn perhaps four inches using a piece one square foot in area.Extra deep drawing may involve the formation of as much as an eight inchdepression in a one square foot sheet of metal.

It is also well known that the concentration of forces is so great inthe cold drawing operation that metallurgical changes are effected incertain steels, usually to the extent that brittleness may be impartedto high carbon steels. On the other hand, high carbon steels such as SAE1020 have increased rigidity or strength so as to resist cold drawingand make the operation much more difficult from the point of view offorces applied as well as wear and tear on the dies. In general, it hasbeen the practice in industry for some time to use carbon steels in theseries SAE 1006 to SAE 1015 (i. e., having about ODS-0.15% C and about0.300.60% Mn) for drawing automobile body and fender stocks, lamps, oilpans, and a number of other deep drawing operations. Steel of this type,usually referred to as mild steel, possessesvery good ductility or theability to withstand cold deformation, but it possesses such ductilityat a sacrifice in strength and rigidity.

Coatings applied to such carbon steels of the type which adhere ratherwell to the carbon steel tend to separate therefrom upon bending orsubsequent treatment of the carbon steel, and particularly upon drawingor actual cold forming of the carbon steel. The same is true of coatingsapplied to the rust-resistant metal sheets which are subsequently coldformed or drawn. There are a vast number of coatings which may beapplied in the art as flexible or deformable coatings, such as resincoatings formed of synthetic resins alone or in paints or varnishes orthe like. In our invention we also use thermoplastic resin coatings,because we have found that preliminary heating step of the coating toapproximately its fusion temperature is of critical importance inobtaining the desired adherence to the base metal. Such coatings aredeformable at least to the extent that they are no more brittle than thecarbon steel sheets here employed (or they are no more'brittle in theform of thin coatings or 'films than the carbon steel sheet hereemployed).' In the practice of the instant invention such coatings areactually softer than the carbon steel sheet and more readily deformable,since such coatings are synthetic resinous coatings which may bedeformed without deformation of the base metal. Notwithstanding thisfact, it appears that such coatings tend to separate from the metalbacking when the same is bent or otherwise formed into a desired shape,if such coatings are not applied and embossed in the manner describedherein.

The instant invention affords a solution to many problems confrontingthe workers in this art. A key to the instant invention resides in theconcept of applying such thermoplastic deformable flexible coatings tothe metal sheeting as an initial treatment, followed first by a bakingor heating operation wherein the coating is briefly raised to its fusiontemperature, and then followed by embossing of the coating (with orwithout embossing of the sheet), before drawing and/ or other secondaryoperations. The combination of heating and embossing of the coatingitself apparently brings about a number of unique and importantadvantages, including distinctly superior adhesion between the coatingand the metal sheet during working of the sheet, as well as changes intemperature of the sheet. Also, it appears that the resin coatingdevelops additional hardness and toughness and resistance to wear andtear. When the metal sheet is also deformed in the embossing operationdistinctly superior adherence is obtained during ordinary wear and tearas well as during a forming operation such as drawing.

An important object of the instant invention is to provide an improvedmethod of applying coating to metal sheets, and further to provide animproved coated metal sheet and articles formed therefrom.

It is a further object of the instant invention to provide an improvedmethod which comprises applying a thin coherent film of deformablethermoplastic coating material to a metal sheet, heating the coating onthe sheet briefly to its fusion temperature, and then cooling thecoating to just below its fusion temperature and embossing the coating.

Other objects, features and advantages of the instant invention willbecome apparent to those skilled in the art from the following detaildisclosure thereof and the drawings attached hereto and made a parthereof.

On the drawings:

Figure 1 is a diagrammatic view showing generally the sequence ofoperations in the coating and embossing steps here employed;

Figure 2 is a fragmentary detail view in elevation (with parts shown insection) of one type of embossing operation embodying the instantinvention;

Figure 3 is a detail fragmentary view in elevation with parts shown insection of another embossing operation embodying the instant invention;and

Figure 4 is a sectional elevational view of an embossed coated sheet ofthe instant invention (such as that shown in Figure 3) which has beendrawn to form a generally dish-shaped article.

As shown on the drawings:

In Figure l, the reference numeral 10 indicates generally an arrangementfor contiuously coating a metal sheet 11 which moves in the directionindicated by the arrow heads. The metal sheet 11, preferably in the formof a carbon steel sheet that is flat and of substantially uniformthickness is unwound from a suitable source- (not shown) and fed past acoater 12, which is here: shown as a device for spraying coatingmaterial c ontothe top of the sheet 11. The coating material is asub-coat which is applied initially in the form of an extremely thinfilm.

Next, the sheet 11 coated with a sub-coat c is passed through a furnace13. In the preferred embodiment of the instant invention, thesub-coating c is applied in the form of a concentrated (75%) mineralspirits solution of polyvinyl chloride in an amount sufficient todeposit a dried resin film on the sheet 11 at the exit of the furnace 13of 0.0005 inch thickness. The sheet 11 is 18 gauge SAE 1010 sheeting.The sheet 11 with the coating c thereon is passed through a furnace 13approximately 40 feet in length at a speed of 15 feet per minute. Thefurnace is maintained at 350 F. which is the fusion temperature of thepolyvinyl chloride resin. As will be appreciated, the coated sheet 11 isin the furnace 13 a relatively short period of time so that the resin issubjected to the fusion temperature only briefly. In this way, the resinreaches its fusion temperature and is con verted momentarily to aviscous liquid, but it does not remain in this state sufficiently longto actually flow freely off the sheet 11, but rather it consolidates thefilm into a coherent uniformly thick resinous film.

At the exit of the furnace 13, the coated sheet 11a is immediatelycooled, which may be accomplished by air cooling as herein indicated orby forced cooling by any of a number of known means. The sheet 11a hasthe sub-coat c thereon in dry cured form and the sheet 11a is thenpassed beneath a second coater 14 which applies the same mineral spiritssolution hereinbefore described onto the sheet 11a as a final coatingmaterial C. In this instance a sufficient amount of coating material Cis applied to add a final film of coating material of 0.004 inchthickness. The sheet 11a is then passed through a second furnace 15 also40 feet in length and also at a speed of 15 feet per minute. The furnace15 is also maintained at 350 F. so as to effect briefly fusion of theresin, as well as complete removal of the mineral spirits. At the exitof the furnace 15 the final sheet 11b (with the sub-coat c and the finalcoating C thereon) is cooled in this case again by exposure to theambient atmosphere. although other known cooling means may be employed.The sheet 11b is cooled to approximately 300 F. and then passed betweenthe embossing rolls 16 and 17 to obtain a final product lie that isembossed. If adequate cooling of the coated sheet 11b cannot beaccomplished by cooling in air or any equally simple means (which isusually the case in the relatively short space available) cooling watermay be fed into the embossing rolls l6 and 17 so as to assure carryingout of the embossing at a temperature at least as low as 300 F. Ingeneral, the temperature should be 300 F. plus or minus 25", at whichforming of the resinous subcoat c and final coating C may be easilycarried out without the application of great pressures or the cutting ofthe film and also without the subsequent loss of the embossed impressionby flow of the resin (if the resin is still too warm).

In general, the embossing step is carried out at 25 to 75 F. less thanthe fusion temperature of the resin for ideal operating conditions. Thesub-coating applied is preferably 0.0001 to 0.001 inch. This sub-coatingc is relatively thin and obtains the full benefit of the heatingoperation in the furnace 13 so as to obtain optimum adherence and flowconditions within the furnace 13. Although it may be possible to applythe entire coating in a single operation, it has been found distinctlysuperior to apply a sub-coating first in the manner herein described andfollow this with the thicker final coating C. It will also beappreciated that in prior art procedures wherein a thin coherent film ofembossed material is caused to adhere to a metal backing sheet, the useof the temperatures herein employed would be impossible because theembossed configuration would be lost through even relativly slow flow ofthe resin at the furnace temperatures. In contrast, this slow flow ofthe resin at the furnace temperatures is here employed to obtain optimumoperataesnava ing conditions for adhesion of the resin. The resin maythus flow into each and every minor surface irregularity in the sheet 11while the sheet passes through the furnace 13 and the final coating C ina furnace 15 may also flow so as to assure uniform coating thickness onthe sheet 11 in the final product 11b. As will be appreciated therelatively small mass of coating applied as the sub-coat can flow morefreely and penetrate better each and every minor surface irregularity inthe sheet 11, because the heat applied tberto in the furnace 13 willmore readily fluidize the resin. Because such a thin film is employed inthe furnace 13, greater fluidization thereof does not cause actual flowof resin off of the sheet 11. On the other hand, the greater mass of thefinal coating C and the greater amount of solvent therein which must beremoved prevents such extreme fiuidization of the coating in the furnace15, although it does permit a sufficient amount of flow to obtain auniform film thickness and also to obtain mutual fusion of the sub coatc and the main coat C which results in the film F indicated in Figure 2.

Referring now to Figure 2, it will be seenthat the finally coated sheetlib with the resin film F thereon passes between the embossing rolls 16and 17. In the embodiment of Figure 2, the bottom roll 17 is a smoothroll which prevents deformation of the metal sheet 11b; whereas the topembossing roll 16 is provided with bosses 16a thereon. As will beappreciated, the bosses 16a can have any desired configuration orarrangement on the surface of the roll 16 so as to emboss or coin thedesired pattern on the film F. ln'general, the bosses 16a are separatedby valleys lab on the surface of the roll 16 and the bosses 16a extendradially outwardly from the valleys 16b a distance 11 ranging from aboutA; to about 4 of the film thickness x, but as here shown the distance his onehalf the film thickness z. The rolls 16 and 17 are spaced apart sothat embossing takes place only on the film F and no deformation of themetal sheet lib is obtained. The thickness x of the metal sheet 11b mayrange from a maximum of about 0.1 inch to a practical minimum of about0.01 inch. Preferably 18 gauge (0.05 inch thickness) or less is used.The resulting embossed coated sheet 110 is provided with correspondingbosses 155a and valleys 13b to conform with the contour of the surfaceof the embossing roll 16 and the embossing process results in additionaladherence between the film F and the metal sheet illc.

in carrying out the coating step in the practice of the instantinvention it will be appreciated that any of a number of well knowncoating methods may be employed and any of a number of well knownsynthetic resinous coating materials may be employed, with or withoutpigments. In each case the thermoplastic coating materials are heated tosubstantially their fusion temperatures for a short period of time, suchas 2 to minutes, so as to obtain the desired cooperation between thecoating materials and the metal base.

Referring now to Figure 3, it will be seen that elements thereincorresponding to elements shown in Figure 2 are given the same ref rencenumerals in the 100 series or are given the same reference letter in theprimed series. In Figure 3 both the upper embossing roll 11.6 and thelower embossing roll 1117 are provided with bosses 116a and 117arespectively with valleys Hub and H712, respectiveiy, spacedtherebetween. The height of the bosses indicated as h for both rolls 116and 117 is substantially the same and is about 0.010 to about 0.014inch. The film thickness 1 and the metal sheet thickness x are the sameas those given for Figure 2; but the height of the bosses h ranges fromto /2 of the overall thickness x plus 1 and is preferably 20 to 45%thereof. In this way deformation of the metal sheet 11112 isaccomplished as well as deformation of the film F.

The embossing operation (with the possible exception of. the overallpressures used) is substantially the same 6 for each of the variouscoating materials and each of the various coated base sheetshereinbefore described. As indicated, carbon steel sheet is preferredfor use in the practice of the instant invention. Such sheet may haveabout 0.05-0.30% C., and preferably has only about 0.30-0.90% Mn. Thisinvolves the steels within the range SAE 1006 to SAE 1030, except forSAE 10l9, 1022, 1024 and 1027 which have higher Mn contents (of as muchas 1.65% Mn). Preferably the Mn content is O.250.60%, using C contentsas high as 0.30%; and in many instances the greatest advantages of theinstant invention are obtained using steels within the range SAE 1006 toSAE 1015 (0.050.15% C and 0.250.60% Mn).

The sheets 11c and 1110 may be cold worked, as by bending or the likewithout separation of the films F and F respectively, therefrom. Inparticular, the sheet lllc embossed on both sides may be used in adrawing operation to advantage. The drawing operation which is employedis, of course, a standard drawing operation of the type well known tothose skilled in the art. The differences here involved include greaterease of drawing, apparently better lubrication between the die and theworkpiece, less wear and tear on the die, a retention of the embossedcontour of the workpiece during the draw ing or forming operation, and aretention of the embossed contour of the coating on the base metalduring the drawing or forming operation. In other respects, the drawingoperation is the same as in an ordinary commercial operation. Drawingitself is a well known art and need not be described herein in detail.For the sake of distinguishing from ordinary bending, stamping orcutting operations, drawing could probably best be defined as involvingthe application of forces to the workpiece that are comparable to forcesat least sufiicient to make a 2 inch depression in a square foot of theworkpiece sheet. xpressed in other terms, drawing involves the shapingof a sheet into a dish-shaped article or an article having a bowedcontour; and the workers in the art generally consider a material hasgood deep drawing quality if it can be drawn 4 inches per square foot.The drawing operation itself involves applying suitably formed male andfemale dies to the sheet material under pressure (at less than thecritical temperature for cold drawing) in order to effect deformationof'the sheet to form the dish-shaped article.

Referring briefly to Figure 4, it will be seen that the embossed sheetsuch as the sheet 1110 (Figure 3) may be drawn to form a generallydish-shaped panel member 19 wherein the central portion 19a is recessedabout 4 inches'as the dimension r indicates, and a'flange-like portion19b is retained around the periphery. The drawing operation isaccomplished in an ordinary drawing press so as to provide a dish-shapedfront panel member 19.

Amongthe coatings which may be employed in the practice of the instantinvention those of the greatest significance are the natural and/orsynthetic resin coatings. Among this group the so-called elastomers arepreferred. The resin or plastic elastomers are well known materials tothose skilled in the art possessing generally elastomeric propertiescomparable to that of natural rubber. Such elastomers include rubber,chlorinated rubber, rubber-synthetic resin admixtures, synthetic rubbers(i. e. butadiene-styrene, isoprene, chloroprene, butadiene-acrylonitrilecopolymers), flexible (or saturated) polyester resins, vinyl chl-oridepolymers, vinyl chloride-vinylidene chloride copolymers, vinylchloridevinyl acetate copolymers, and the like. These resin or elastomercoatings may be applied per se as by fiamespraying, which isparticularly effective with polyethylene and polytetrafiuoroethylene(which are well known elastomers), or the resins may be applied insolution in organic solvents with subsequent baking operations to removethe solvent, or the resins may be applied in .cmulsion form in aqueousmedia also the subsequent drying to remove the carrier. Solutions oremulsions of the resins may be applied by spraying, dipping, painting,or the like. Special treatments for the metal surface prior to theapplication of such resins may also be employed, such as thebonderizing, or Parkerizing processes. Pigments may be included oromitted as desired, but since decorative effect is an important featurein many uses of the invention, various colored pigments are usuallyincluded so that an elastomer base paint is preferred in many instances.Specific examples of coatings include the following:

(1) Vinyl chloride (95%)vinylidene chloride (5%) commercial grade mediumcopolymer is applied from a mineral spirits solution to 18 gauge SAE1010 sheeting by spraying on followed by baking at 350 F. to dry andcure the coating, in an operation which invol e; applying first 0.0005inch of copolymer, followed by the subsequent application of 0.005 inchof copolymer and the procedure hereinbefore described and excllentadherence is obtained between the resulting films and the base metalsheet after embossing on the film side only or embossing on both sides.

(2) A sub-coating is applied to 20 gauge SAE 1010 sheeting in the formof 0.0005 inch of vinyl chloride (95 %)-vinylidene chloride (5%)commercial grade medium copolymer which is baked at 350 F. to dry andcure the same, and a main coating of paint containing green pigments andthe vinyl chloride vinylidene chloride medium copolymer is then appliedin a film thickness of 0.004 inch followed by baking at 350 F. to dryand cure the coating. As indicated, the baking step in each case in theprocedures of paragraphs (1) and (2) herein is carried out for threeminutes.

(3) Polyethylene is flame-sprayed onto a 0.050 inch thick 188 stainlesssteel sheet to provide a sub-coating of 0.001 inch average thickness,which is heated to 425 F. for three minutes; and a second polyethylenecoating of 0.005 inch average thickness is flame-sprayed on and bakedfor three minutes at 425 'F.; and it is noted that superior adherencebetween the polyethylene coating and the metal backing is obtained afterembossing both sides of the coated sheet (even though it is recognizedthat polyethylene has relatively poor adherence to any other material).

(4) A procedure is carried out that is the same as that described inparagraph (2) except that the resin used in the case of both coatings isvinyl chloride (95% )-vinyl acetate (5%) copolymer and the bakingtemperatures used are 325 F.

(5) Successive coatings of 0.0005 and 0.005 of commercial flexiblepolyester resin (i. e. ethylene glycol propylene glycol-phthalate) invarnolene solution are painted onto 20 gauge SAE 1010 sheeting andsuccessively baked for three minutes each at 250 F.

Each of the foregoing coated sheets is embossed on the film side in themanner hereinbefore described using an embossing roll having bossesthereon of an average height of 0.002 inch and on both sides usingembossing rolls having bosses thereon of an average height of 0.012 inchand it is found that the embossed sheets may be bent back and forthwithout causing the resin coating thereon to crack or separate from themetal.

It will be understood that modifications and variations may be effectedwithout departing from the spirit and scope of the novel concepts of thepresent invention.

We claim as our invention:

1. A method of producing a coated sheet metal stock capable of beingcold formed which comprises applying a thin coherent film of deformablethermoplastic synthetic elastomeric resinous coating material to a metalsheet, heating the film on the sheet briefly to its fusion temperatureto fuse the film together and onto the sheet, then cooling the film tobelow its fusion temperature, next applying to said film a layer ofdeformable thermoplastic synthetic elastomeric resinous coating materialthat is adherent to said film on the sheet and heating said layerbriefly to its fusion temperature to accomplish mutual fusion of thelayer and film, then cooling the layer to just below its fusiontemperature, and finally pressure embossing the coating at just belowits fusion temperature.

2. The method claimed in claim 1 wherein said film and said layer of thecoating are each formed of polyethylene.

3. The method of claim 1 wherein said film and said layer of the coatingare each formed of a polyvinyl resin.

4. The method of claim 1 wherein the metal sheet is carbon steel sheet.

5. A method of producing a coated sheet metal stock capable of beingcold formed which comprises applying a thin coherent film of 0.001 to0.0001 inch thickness of polyvinyl chloride resin to a carbon steelsheet, heating the film on the sheet briefly to its fusion temperatureat 350 F. to fuse the film together and on to the sheet, then coolingthe film to below its fusion temperature, next applying to said film alayer of 0.01 to 0.001 inch thickness of polyvinyl chloride resin andheating said layer briefly to its fusion temperature at 350 F. toaccomplish mutual fusion of the layer and film, then cooling the layerto just below its fusion temperature, and finally pressure embossing theresinous coating at just below its fusion temperature without deformingthe metal sheet.

References Cited in the file of this patent UNITED STATES PATENTS2,030,066 Ienett Feb. 11, 1936 2,270,662 Raney Jan. 20, 1942 2,530,738Spessard Nov. 21, 1950 FOREIGN PATENTS 574,157 Great Britain Dec. 21,1945

1. A METHOD OF PRODUCING A COATED SHEET METAL STOCK CAPABLE OF BEINGFORMED WHICH COMPRISES APPLYING A THIN COHERENT FILM OF DEFORMABLETHERMOPLASTIC SYNTHETIC ELASTOMERIC RESINOUS COATING MATERIAL TO A METALSHEET, HAVING THE FILM ON SHEET BRIEFLY TO ITS FUSION TEMPERATURRE TOFUSE THE FILM TOGETER AND ONTO THE SHEET, THEN COOLING THE FILM TO BELOWITS FUSION TEMPERATURE, NEXT APPLYING TO SAID FILM A LAYER OF DEFORMABLETHERMOPLASTIC SYNTHETIC ELASTOMERIC RESINOUS COATING MATERIAL THAT ISADHERENT TO SAID FILM ON THE SHEET AND HEATING SAID LAYER BRIEFLY TO ITSFUSION TEMPERATURE TO ACCOMPLISH MUTUAL FUSION OF THE LAYER AND FILM,THEN COOLING THE LAYER TO JUST BELOW ITS FUSION TEMPERATURE, AND FINALLYPRESSURE EMBOSSING THE COATING AT JUST BELOW ITS FUSION TEMPERATURE.